Check out the fall issue of Ontario Pipeline Magazine for an article about Online peCOD being used for control and prevention of the formation of harmful disinfection by-product formation in drinking water treatment. See an excerpt from the article below:

Safe operation of a Water Treatment Plant (WTP) requires careful monitoring of the water supply influent to the plant, as a guard for any substances entering the treatment works that could negatively impact treated water quality in the distribution system. One aspect of water quality that has recently garnered more attention from authorities and utilities is Natural Organic Matter (NOM), which refers to a group of carbon-based compounds found in natural water systems formed by the decomposition of organic materials and associated metabolic reactions.

While NOM itself does not pose a risk to human health, some NOM compounds are known to react with chlorine and chloramines in drinking water treatment to produce disinfection by-products (DBPs) such as Trihalomethanes (THMs) and Haloacetic Acids (HAAs), which are known to be carcinogenic and/or genotoxic (Figure 1). Health Canada, the US Environmental Protection Agency, and the World Health Organization include sections focused on control of DBPs in their Drinking Water Treatment Guidelines.

Disinfection By-Product Formation Pathway

Preventing the formation of DBPs is a multi-faceted issue for drinking water utilities, with a variety of strategies being developed for both general treatment and specific plant/source conditions. Each facility and water source is different, therefore no one strategy can be applied across the board, and often utilities are encouraged by their local authority to have a unique monitoring plan developed. Prevention strategies can be generalized into four groups:

Using a different chemical disinfectant with less tendency to form by-products;

Using a non-chemical disinfectant; and/or

Removing DBPs prior to distribution.

Since drinking water plants typically maintain a disinfectant residual in the distribution system, use of solely a non-chemical disinfection is often not an option. Similarly, most guidelines specify chlorine or chloramines for disinfection, therefore it can be difficult and costly to switch to a different chemical disinfectant. Removal of DBPs before distribution is often not practical, due to high implementation costs and uncertainty as to whether the DBPs are forming at the plant or in the distribution system through reactions with residual disinfectant. Therefore, the preferred prevention strategy for most utilities is optimization of treatment conditions to remove the precursor NOM compounds.